Processes of obtaining direct positive images by processing internal latent image type silver halide photographic emulsions with a surface developer in the presence of a fogging agent as well as silver halide photographic emulsions and photographic materials used for such processes are disclosed in, for example, U.S. Pat. Nos. 2,456,953; 2,497,875; 2,497,876; 2,588,982; 2,675,318; 3,227,552; and 2,592,250; British Pat. Nos. 1,151,363; and 1,011,062; Japanese Patent Publication No. 29,405/'68, etc. By an internal latent image type silver halide photographic emulsion is meant a silver halide photographic emulsion having photosensitive nuclei mainly in the inside of silver halide grains and forming latent images mainly in the inside of the silver halide grains caused by the internal photogsensitive nuclei. A photographic emulsion composed of such silver halide grains is not substantially developed by a surface developer.
By the term "surface developer" is meant a developer which develops a surface latent image of silver halide grains but substantially does not develop an internal latent image. A surface developer or the composition thereof usually contains a conventional silver halide developing agent but must not substantially contain a silver halide solvent (e.g., a water-soluble thiocyanate, a water-soluble thiosulfate, ammonia, etc.) used for forming internal latent images. For the surface developer, it is preferred to use slightly excessive amount of halide or the excessive halide can be incorporated in a silver halide emulsion as a halide-releasing compound. However, the use of a large amount of halide shall usually be avoided for preventing the substantial decomposition or dissolution of silver halide grains.
In the above-described process of obtaining a direct positive image, a fogging agent may be incorporated in a developer or may be incorporated in a silver halide photographic emulsion layer of a photographic material or other layer thereof.
In a silver halide photographic material, silver halide photographic emulsions are ordinary spectrally sensitized.
For employing the foregoing process of obtaining a direct positive image in the presence of a fogging agent in many application fields regarding photography, improvements of various photographic characteristics such as the improvement of photographic speed, the improvement of the maximum density (Dmax), the reduction of the minimum density (Dmin), the suppression of the occurrence of re-reversal images, etc. have been desired.